Originally Posted by BAGoldBoy
Take the SkyBus from just outside the terminal, runs every 10-15 minutes, takes 15 minutes and costs about A$15 one way. Drops you at the edge of the CBD but only a 10-15 minute walk to the centre or you can take a shuttle bus. Taxi is IIRC about A$40 one way
I'd suggest taking one step further. The SkyBus offers free shuttles from the CBD station (Spencer Street or something) to central CBD hotels. Just get one of them to drop you off to a hotel close to the first thing you want to do, e.g., somewhere along the river.
Since you won't be staying in a hotel, you'll just need to find your own way back to Spencer Street station, but a short taxi ride can solve that problem. (The shuttle back to the station is normally booked by the hotel on your behalf.)
Also, buy a return ticket for the SkyBus, it's slightly cheaper than 2 one-ways. Pick up a free guide book at the ticket booth, it has good discount vouchers for various tourist attractions.